Amethyst, citrine, and ametrine are mineral twin brothers. For all the similarities laid out for the twins, they also have differences. Let’s face it: not all amethysts are born written by handsome men. Often, only the ennobling of amethyst gives him the opportunity to become a sought-after gem.
The color of amethyst depends on the presence of metal ions in the crystal structure of the mineral. Since the geometric dimensions of an atomic space not filled with matter are different, metal atoms act as a kind of interference grating, that is, filters that transmit light with a certain wavelength.
The wavelength of light transmitted by atoms of metallic impurities dispersed in crystals of silicon dioxide gives color to the stone.
Heating changes the internal energy of atoms, which is externally expressed in a change in the size of the “gaps” through which light waves of one or another length freely pass. That is why faint natural amethysts easily change color after calcination.
The practice of ennoblement amethyst gives amazing results. Having reached a temperature in the range close to 500 ° C, the mineral acquires a bright yellowness. In fact, amethyst turns into citrine. A further increase in the temperature of the stone thickens the color: at 575 ° C, the amethyst becomes red-orange, sometimes with brown tones.
Natural stones of this color – due to their rarity – are highly valued by jewelers and collectors. At the same time, none of the modern gemologists build illusions regarding the full naturalness of the color of orange citrines sold in stores…
Not every amethyst tends to turn yellow when heated or irradiated. Separate American and African amethyst deposits produce crystals that tend to turn green when heated to 450 ° C.
Citrines (yellow amethysts) also often require human intervention in the centuries-old history of crystal formation. The refinement of citrine is carried out in exactly the same way as bringing the amethyst to condition. Only color targets are slightly different. Natural citrines – like amethysts – may have insufficient color intensity, weak severity of shades. Therefore, the thermal and radiation refinement of citrines is aimed at thickening the color, giving it rarely found in natural variations.
The chain of transformations experienced by dyed silicon oxide metal ions, when the temperature reaches 600 ° C and above, leads to the appearance of the effect of milk opacity of the crystal.
The heterogeneities of the stone create the effect of the play of light, similar to opalescence. Sometimes color overflows have a pronounced blue dominance – such an amethyst (still amethyst!) Can serve as material for imitating a moonstone.
Incidentally, the thermal effect on amethyst is sometimes reversible. Brazilian gems, heated to a complete loss of their original color, after six months of exposure, gradually restore their natural appearance.
Demand for bicolor amethyst citrines is growing by leaps and bounds. The buyer knows that artificially colored stones are brighter and more contrasting than their natural counterparts. However, the low price and aesthetic splendor of the finished product makes the refinement of ametrines more and more frequent.
The effect of semiprecious bicolor is achieved by a combined effect on quartz. The standard sample is usually the stone mined in the mines of Bolivia. The zonal distribution of irradiation with a hard-spectrum spectrum and the usual infrared rays gives us the result in the form of impeccable jewelry raw materials for the production of two-color faceted inserts.
It makes no sense to apply risky technology to an expensive stone. The twenty-fold price difference between synthetic ametrine and natural ametrine makes any “decoration” of a natural gem unnecessary.
Moreover, the exquisite pallor of the natural color of natural ametrine is well recognized – and appreciated! – In aristocratic circles around the world. Generally, this type of stones is used in metaphysical jewelry.